JPH0564854B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for manufacturing a lead frame used for fixing semiconductor chips such as ICs and LSIs.

[Background technology]

2. Description of the Related Art Conventionally, metal lead frames have been used to assemble semiconductor devices in which semiconductor chips are integrated with a resin mold and have a plurality of protruding pins.
This lead frame 10 is formed by punching out a thin metal plate with a press or by etching, and its shape is as shown in FIG. a tab lead 3, a plurality of fingers 4 whose inner ends face the periphery of the tab 2, and a frame portion 5 that supports these fingers 4 and the outer ends of the tab lead 3.
and sprocket holes 6 provided at regular intervals along both side edges of the frame portion 5.

To assemble a semiconductor device using such a lead frame 10, first, the semiconductor chip 1 is mounted on the tab 2, and then each electrode of the semiconductor chip 1 and the corresponding inner end of the finger 4 are connected with wires or wires. After that, the inner region of the rectangular frame portion 5 is molded with synthetic resin to cover the semiconductor chip 1, and then the frame portion 5 is cut out to obtain a flat lead or in-line type semiconductor device.

However, in the above semiconductor device, it is extremely difficult to connect the fingers 4 of the lead frame 10 and the electrodes of the semiconductor chip 1. Recently, the number of pins of semiconductor devices, that is, the number of fingers 4 of the lead frame 10 has increased, and due to miniaturization, the distance between adjacent fingers 4 has become smaller, and the width of the fingers 4 themselves has become narrower. The efficiency and reliability of connection work has become a factor that cannot be ignored in relation to product cost. Therefore, as shown in FIG. 7, when the aluminum electrode 8 formed on the silicon 7 is thinner than the protective film 9 formed on the silicon surface and is formed inside the semiconductor chip 1, Conventionally, a bump 4a is provided at the tip of the finger 4 that is connected to the electrode 8 to ensure contact, but the finger 4 has a bump 4a formed by press bending. This is extremely difficult because the width, diameter, etc. are extremely small, and etching is not preferred in terms of cost.

In particular, when bonding the bumps 4a to the electrodes 8 of the semiconductor chip 1, if the amount of crushing deformation of the bumps during the pressing process is not uniform for all bumps, the fingers 4 are likely to shift laterally and come abnormally close to the adjacent fingers 4, which will reduce the yield. will be low. In order to suppress this, the fingers 4 must be made thicker, but this requires an increase in the pressing and bending force of the fingers during pressing, which is not preferable for the semiconductor chip 1.

[Purpose of the invention]

The present invention has been made in view of the above points, and an object of the present invention is to provide a method for manufacturing a lead frame in which a bump can be easily formed at the tip of a finger without coming into contact with an adjacent finger. That is.

[Summary of the invention]

In order to achieve the above object, the present invention press-forms only the middle part of the finger with the finger base side of a lead frame molded to a desired thickness being preloaded. In addition to making it wider than the section,
This device is characterized in that a bump is formed at the tip of the finger for connection to an electrode of a semiconductor chip.

As a result, the bump at the tip of the finger is formed as a protrusion with a desired height because the pressed middle part becomes a thin part.

In addition, by pressing and crushing the middle part, a wider area is formed in that part than the finger base side and the finger tip part, so the resistance against lateral slippage of the finger is strengthened, and it is possible to prevent the finger from coming into abnormal proximity with the neighboring finger. Therefore, the yield can be improved.

〔Example〕

FIG. 1 is a partially sectional perspective view of a lead frame 10 manufactured according to an embodiment of the present invention.

The lead frame 10 is made of nickel or other conductive metal thin film laminated on a film 11 made of synthetic resin such as polyimide or polyester.
As in the conventional example, a rectangular tab 2 to which a semiconductor chip 1 is attached, four tab leads 3 supporting the tab 2, a plurality of fingers 4 whose inner ends are exposed to the periphery of the tab 2, and these fingers 4 and the tab leads 3. and a frame portion 5 supporting the outer end of the film 11.
A device hole 12 is bored at a position facing the tab 2 of
A sprocket hole 6 is formed as a positioning hole for assembling and transporting the lead frame 10.

FIG. 2 is a diagram showing the molding process of this lead frame. First, as shown in FIGS. a to b, a device hole 12 is formed in a film 11 made of a synthetic resin such as polyimide or polyester by pressing using the pushback method. The pushback method is a processing method in which a desired portion is first punched out using a pressing die as shown in Fig. A, and then the receiving die is raised again to fit and hold the cutout piece 11a in the device hole 12 that has been previously drilled as shown in Fig. B. Therefore, after processing, the film 11 is maintained in the state shown in FIG. b in which the device holes 12 are not opened, and can be handled as a single sheet. Incidentally, when forming the device hole 12, other windows such as the sprocket hole 6 can also be formed at the same time.

Next, a conductive metal layer 13 such as copper is formed on the unopened film 11 by means of electroless plating, vapor deposition, etc., as shown in FIG. Furthermore, a photoresist layer 14 is coated on the conductive metal layer 13 as shown in figure d, and by applying a photomask and exposing to light in a desired pattern, cleaning is performed to remove only the exposed areas, resulting in a resist layer 14 as shown in figure e. layer 1
The conductive metal layer 4 formed on the conductive metal layer 13 after pushback and the photoresist layer function as a temporary fixing means to prevent the cutout piece 11a from falling off unnecessarily, and it is similar to a film. It is particularly effective for temporarily fixing thin objects that tend to fall off, such as push-backed objects.

Next, this finger 11 is subjected to a peeling treatment using selenite, caustic soda, etc., and a metal such as nickel is electroformed, so that the resist layer 14 is not formed on the conductive metal layer 13, as shown in figure f. A lead frame 10 having a desired pattern is formed.

When electroforming lead frames with metals such as nickel, use a brightening agent of 0.07% or less (carbon is 0.01~
0.04%, sulfur 0.01~0.04%, and the total of these is
0.07% or less) is used. The brightener content is usually around 0.1%, but when the content is this high, the temperature of the lead frame increases when it is bonded to an IC chip, causing nickel to become brittle. Therefore, it is necessary to limit the brightener content to 0.07% or less. Furthermore, if no brightener is contained, sufficient mechanical strength cannot be obtained, and deformation during processing may cause short circuits with adjacent leads.

After electroforming, by removing the resist layer 14 and then pulling out the cutout piece 11a that closes the window including the device hole 12, a lead frame 10 having a cross section as shown in Fig. g is formed on the synthetic resin film 11. It is. In this case, since the conductive metal layer 10 has a thickness of about 5 to 10 μm, for example, to ensure conductivity for electroforming, the pulling force is small and the lead frame 13 is not deformed. do not have.

Note that in the above embodiment, the lead frame 1
0 is formed on the synthetic resin film 11, but instead of the synthetic resin film 11, a conductive metal stainless steel film or the like may be used.

In this case, there is no need to newly provide the conductive metal layer 13 made of copper or the like as shown in FIG.
It is possible to form a photoresist layer 14 on a stainless steel film 11 and form a lead frame 10 made of nickel on the stainless film by direct electroforming.

The fingers 4 of the lead frame obtained in this state have a constant thickness of about 70 μm. Therefore, only the positions indicated by broken lines in FIG. 3 are pressed.
That is, as shown in FIG. 4, the frame portion 5 and fingers 4 of the lead frame 10 are
The second upper mold C, which is movably provided with respect to the upper mold A, is slightly lowered while applying a preload to the base portion 4b of the second upper mold C. As a result, as shown in FIGS. 5a and 5b, a thin part 4c is formed in the middle part of the finger 4 to be somewhat wider, and a bulging bump is formed at the tip of the finger which is not pressed by the upper and lower molds. 4a is formed simultaneously. The height of this bump 4a (step difference between the top surface of the thin part 4c and the top surface of the bump 4a) is generally 12 to 15μ.
A certain degree is fine.

When connecting the bumps 4a to the electrodes of the semiconductor chip 1, a load is applied to the fingers 4 due to the mounting position of the semiconductor chip 1 and dimensional errors of the lead frame. Since it is sufficiently flexible, it can absorb these dimensional errors and can be connected to the electrodes without disconnection. Furthermore, by pressing from the side of the bump that connects to the semiconductor chip 1, the thin wall portion 4c is warped toward the bump after pressing, so that the bump portion protrudes from the finger 4 toward the semiconductor chip, making the connection easier. ing.

In the above embodiment, the entire lead frame was formed by electroforming, but the present invention is not limited to this, but can also be applied to lead frames integrally formed by press molding, etching, etc. is clear.

Furthermore, when electroforming a lead frame from a metal such as nickel, it is also possible to create a lead frame in which two layers, a layer that does not contain a brightening agent and a layer that contains a brightening agent, are superimposed. If electroforming is performed without adding a brightener, the surface will be roughened and have significant irregularities, which will likely cause temperature concentration when bonding with an IC chip, especially when bonding under pressure.
Bonding can be ensured. On the other hand, if a layer containing a brightening agent is provided on the side opposite to the bonding surface, mechanical strength as a lead frame can be ensured. Note that it is preferable to limit the content of the brightener to 0.07% or less, as described in the above example.

〔Effect of the invention〕

As described above, in the present invention, since the middle part of the finger is pressed to form the bump, molding is easy and it can be used for a lead frame having a large number of fingers. At the same time, the middle part of the finger becomes thinner, which increases the flexibility of the finger, and when connecting semiconductor chip electrodes and bumps, it is possible to absorb mutual misalignment and ensure a reliable connection. .

In addition, by pressing and crushing the middle part, a wider area is formed in that part than the finger base side and the finger tip part, so the resistance against lateral displacement of the fingers is stronger, and the fingers do not get abnormally close to the neighboring fingers. , yield can be improved.

[Brief explanation of the drawing]

Fig. 1 is a partial perspective view showing a lead frame according to an embodiment of the present invention, Fig. 2 is a diagram illustrating a part of the lead frame manufacturing process of the embodiment, and Fig. 3 is a bump formation in the lead frame manufacturing process of the embodiment. FIG. 4 is a sectional view illustrating the pressing operation in the lead frame manufacturing process of the example, FIGS. 5 a and 5 b are sectional views and perspective views showing the finger shape in the example, FIG. 6 is a plan view showing a general lead frame shape, and FIG. 7 is a sectional view showing the relationship between bumps and electrodes of a semiconductor chip. 1...Semiconductor chip, 4...Finger, 4a...
...Bump, 4b...Base, 4c...Thin wall part, 8...
...electrode, 10...lead frame.

Claims (1)

[Scope of Claims] 1. A method for manufacturing a lead frame made of metal foil having a plurality of fingers extending inward from the inner edge of a device hole in which a semiconductor chip is placed, the lead frame being formed to a desired thickness. With the finger base side of the lead frame preloaded, only the middle part of the finger is press-formed, and this middle part is made thinner and wider than the finger base side and the finger tip part, and the finger tip part is equipped with a semiconductor chip. A method for manufacturing a lead frame for a semiconductor device, characterized in that a bump is formed for connection to an electrode.